Diseases of the gastrointestinal tract cause significant morbidity and mortality among children. In developing countries, episodes of infectious diarrhea, including those associated with HIV/AIDS, are major causes of death. In industrialized countries, children with short bowel syndrome suffer from chronic diarrhea requiring treatment with parenteral and enteral nutrition. This revised application requests a mid-career investigator award in patient-oriented research (K24) for Christopher Duggan, MD, MPH. Dr. Duggan's overall research goal is to improve clinical outcomes in diarrheal diseases. He has a record of high productivity in funded research in the fields of nutrition, gastroenterology, and international health. Dr. Duggan has a sound track record of mentoring and excellent opportunities to work with junior investigators. He is Director of Clinical Research in the Division of Gastroenterology and Nutrition at Children's Hospital, Boston (CHB), a faculty member of the CHB Clinical Research Program, a member of the NIH-supported Harvard Digestive Diseases Research Center, and Associate Professor of Pediatrics at Harvard Medical School and of Nutrition at the Harvard School of Public Health. Trainees who are supported by two T32 training programs are available as mentees. The proposed research in this K24 award extends Dr. Duggan's ongoing studies, including an NICHD-supported R01 grant that seeks to evaluate the efficacy of micronutrient supplementation in Tanzanian children at risk of diarrhea. He and colleagues will conduct a randomized clinical trial: 1. To determine whether zinc or micronutrient supplementation has an enteropathogen species-specific effect in preventing gastrointestinal infections in Tanzanian children; and 2. To determine whether routine zinc supplementation reduces measures of iron status in Tanzanian children, compared to micronutrient supplements without zinc. This application offers a combination of a highly successful researcher in a supportive and intellectually rich environment. This mid-career investigator award is needed to protect Dr. Duggan's time to mentor beginning investigators in patient-oriented nutrition research and to expand his research in diarrheal diseases.)